Re: MMX performance....

David S. Miller (
Thu, 6 Feb 1997 14:01:38 -0500

Date: Thu, 6 Feb 1997 17:36:51 +0200 (EET)
From: Hannu Savolainen <>

Is it allowed to use FPU/MXX inside kernel? I recall that this is
not possible since kernel doesn't save FPU state when swiching
between kernel and user modes. Or am I just misunderstood this.

This issue was already hashed out. You must save and restore the fpu
around the memcpy using the FPU, and therefore you weight whether or
not to do the FPU based copy using the size of the area to memcopy.